In order to meet wireless data traffic demands that have increased after 4th generation (4G) communication system commercialization, efforts to develop an improved 5th generation (5G) communication system or a pre-5G communication system have been made. For this reason, the 5G communication system or the pre-5G communication system is called a beyond 4G network communication system or a post long term evolution (LTE) system.
In order to achieve a high data transmission rate, an implementation of the 5G communication system in a mmWave band (for example, 60 GHz band) is being considered. In the 5G communication system, technologies such as beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), an array antenna, analog beam-forming, and a large scale antenna are discussed to mitigate a propagation path loss in the mmWave band and increase a propagation transmission distance.
Further, technologies such as an evolved small cell, an advanced small cell, a cloud radio access network (cloud RAN), an ultra-dense network, device to device communication (D2D), a wireless backhaul, a moving network, cooperative communication, coordinated multi-points (CoMP), and interference cancellation have been developed to improve the system network in the 5G communication system.
In addition, the 5G system has developed advanced coding modulation (ACM) schemes such as hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC), and advanced access technologies such as filter bank multi carrier (FBMC), non orthogonal multiple access (NOMA), and sparse code multiple access (SCMA).
Further, various communication systems including a wired or wireless communication system use a low-density parity-check (LDPC) encoding scheme as a channel coding scheme. An LDPC code corresponds to an error correction code that has practically implementable encoding/decoding complexity and a capability close to a channel capacity which is a theoretical communication limit. The LDPC code may be designed to have a structure suitable for parallel processing and is applied and used for various communication systems such as Institute of Electrical and Electronics Engineers (IEEE) 802.11n/ad Wi-Fi, IEEE 802.16e WiMAX, digital video broadcasting (DVB)-S2/T2/C2 corresponding to a digital broadcasting standard, Advanced Television Systems Committee (ATSC) 3.0, and home network G.hn due to an excellent error correction capability on various actual channels.
As it is well known, a binary LDPC code is defined by a parity-check matrix consisting of elements 0 and 1. When it is assumed that numbers of rows and columns of the parity-check matrix are N and M, respectively, an LDPC encoding scheme using the parity-check matrix receives message bits (information bits) having a length of K=N−M and generates a codeword (encoding bits or bits of a encoding block) having a length N.
The LDPC code is classified as one type of a block code. The block code is designed to support one predetermined code rate and controls the code rate through the use of puncturing as necessary. However, when the code rate is controlled simply through the use of puncturing, there is a disadvantage in that the performance significantly deteriorates compared to the code designed to be suitable for the corresponding code rate. Accordingly, in order to support various code rates with excellent performance in a communication system, designing and using different LDPC codes according to the code rates to be supported may be the simplest solution method. However, storing and using all the LDPC code(s) corresponding to a number of the code rate(s) to be supported creates a big burden in hardware to both a transmitter and a receiver in the communication system.
To solve the problem, research on an rate compatible (RC) LDPC (RC-LDPC) has been conducted by many research groups. An RC-LDPC encoding is one type of LDCP encoding schemes that may effectively support an encoding of various code rates through one encoding structure. In the encoding scheme based on the RC-LDPC, LDPC codes of various code rates may be effectively generated through puncturing and, organically, incremental redundancy (IR) hybrid automatic repeat and request (HARQ) (IR-HARQ) may be supported.
In the conventional RC-LDPC encoding scheme, a high code rate LDPC code part and a low code rate LDPC code part are designed to be concatenated. Further, the low code rate LDPC code part is designed in consideration of supporting of code rate-compatibility. The RC-LDPC code extension method according to the related art is largely divided into a diagonal extension scheme and a general extension scheme according to a scheme of generating parity bits of the low code rate LDPC code part. For example, the general extension scheme includes a lower triangular extension scheme.
FIG. 1 illustrates a structure of a parity check matrix of an RC-LDPC code designed through a diagonal extension used in the RC-LDPC encoding scheme according to the related art.
Referring to FIG. 1, a reference numeral 101 indicates an information area of message bits corresponding to information bits, a reference numeral 103 indicates a first parity bit area of first parity bits for information bits, and a reference numeral 105 indicates a second parity area of second parity bits for information bits. In FIG. 1, “A” indicates a sub-matrix for the information bits, and “B” indicates a sub-matrix for the first parity bits. Further, a reference numeral 107 indicates a design free area in which “1” can exist in the parity check matrix. As illustrated in FIG. 1, in the parity check matrix of the RC-LDPC code designed through the diagonal extension, the second parity bit area (reference numeral 105) corresponds to a rate-compatible parity area and is designed by a diagonal matrix. When the high-code rate parity check matrix of the RC-LDPC code is H0, the parity check matrix HD of the RC-LDPC code designed through the diagonal extension may be expressed by Equation 1 below.
                              H          D                =                  [                                                                      H                  0                                                            0                                                                                      B                  D                                                            I                                              ]                                    Equation        ⁢                                  ⁢        1            
In Equation 1 above, I denotes a diagonal matrix and BD denotes a sub-matrix which may be configured in a general form. Further, 0 denotes a zero matrix. Since parts H0, 0, and I are all fixed in HD, optimization of HD may be achieved by optimization of the sub-matrix BD. As described above, an encoding of the RC-LDPC code designed through the diagonal extension includes two concatenated encodings. First, a codeword is acquired through the encoding of the LDPC code defined as H0. Further, a final codeword is acquired by receiving the codeword and performing a single parity-check (SPC) encoding defined as [BD;I]. A transmitter punctures the remaining parity bits except for parity bits corresponding to transmission code rates in the codeword and transmits the codeword.
FIG. 2 illustrates a parity check matrix structure designed through a lower triangular extension used in the RC-LDPC encoding scheme according to the related art.
Referring to FIG. 2, a reference numeral 201 indicates an information area of message bits corresponding to information bits, a reference numeral 203 indicates a first parity bit area of first parity bits for information bits, and a reference numeral 205 indicates a second parity area of second parity bits for information bits. In FIG. 1, “A” indicates a sub-matrix for information bits, and “B” indicates a sub-matrix for the first parity bits. Further, a reference numeral 207 indicates a design free area in which “1” can exist in the parity check matrix. As illustrated in FIG. 2, in the parity check matrix of the RC-LDPC code designed through the general extension, the second parity bit area (reference numeral 205) corresponds to a rate-compatible parity area and the rate-compatible parity area is designed by a general lower triangular matrix. When the high-code rate parity check matrix of the RC-LDPC code is H0, the parity check matrix HG of the RC-LDPC code designed through the general extension of FIG. 2 may be expressed by Equation 2 below.
                              H          G                =                  [                                                                      H                  0                                                            0                                                                                      B                  G                                                            T                                              ]                                    Equation        ⁢                                  ⁢        2            
In Equation 2 above, T denotes a lower triangular matrix and BG denotes a sub-matrix in the parity check matrix which may be configured in a general form. Since H0 and 0 are fixed in HG, designing to optimize HG is the same as designing to optimize BG and T. As described above, an encoding of the RC-LDPC code designed through the general extension may be implemented by two schemes.
In the two encoding schemes of the RC-LDPC code designed through the general extension, the first scheme calculates an inverse matrix of the matrix T and calculates matrix-multiplication. First, a codeword is acquired through an encoding of the LDPC code defined as H0. A final codeword may be acquired by multiplying the codeword and T−1BG.
FIG. 3 illustrates a procedure by the first scheme corresponding to an encoding process using matrix-multiplication of a general extension RC-LDPC code according to the related art. Based on the first scheme, for example, encodings 301 and 303 by two concatenated LDPC codes are performed.
Referring to FIG. 3, x briefly indicates an area including an information area and a first parity area, p1/3 and p1/4 indicate second parity areas, A, B, C, and D briefly indicate sub-matrixes of the parity check matrix, and subscripts 1/2, 1/3, and 1/4 indicate, for example, corresponding code rates.
The second scheme of the two encoding schemes of the RC-LDPC code designed through the general extension sequentially performs SPC encodings for all rows of the matrix T corresponding to the lower triangular matrix. First, a codeword is acquired through an encoding of the LDPC code defined as H0. Then, SPC encodings are sequentially performed for the rows of the LDPC code defined by the matrix [BG;T]. Accordingly, based on the second scheme, encodings of the LDPC code defined as H0 and SPC codes corresponding to a number of rows of the matrix [BG;T], which are concatenated, are performed.
FIG. 4 illustrates an encoding process using concatenated SPC encodings of the general extension RC-LDPC code according to the related art. Meanings of the reference numerals of FIG. 4 are the same as those of FIG. 3 and a reference numeral 401 indicates the sequentially performed concatenated SPC encodings.
However, when the encoding and decoding scheme using the parity check matrix of the RC-LDPC code designed through the diagonal extension or the parity check matrix of the RC-LDPC code designed through the lower triangular extension is implemented, complexity for the encoding or the decoding may increase and thus a method of reducing the complexity is required.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.